PRODUCTION OF PSEUDOMONAS-AERUGINOSA RHAMNOLIPID BIOSURFACTANTS IN HETEROLOGOUS HOSTS

The high-level production of rhamnolipid biosurfactants is a unique fe ature of Pseudomonas aeruginosa and is strictly regulated in response to environmental conditions. The final step in rhamnolipid biosynthesi s is catalyzed by the rhlAB genes encoding a rhamnosyltransferase. The expression of the cloned rhlAB genes was studied in heterologous host s, either under the control of the rhlR and rhlI rhamnolipid regulator y elements or under the control of the tac promoter. A recombinant P. fluorescens strain harboring multiple plasmid-encoded copies of the rh amnolipid gene cluster produced rhamnolipids (0.25 g liter(-1)) when g rown under nitrogen limiting conditions. The highest yields (0.6 g lit er(-1)) and productivities (24 mg liter(-1) h(-1)) were obtained in a recombinant Pseudomonas putida strain, KT2442, harboring promoterless rhlAB genes fused to the tac promoter on a plasmid. Active rhamnosyltr ansferase was synthesized, but no rhamnolipids were produced, by recom binant Escherichia coli upon induction of rhlAB gene expression.